Fixed-time Trajectory Tracking Control Of Autonomous Underwater Robots

With the development and progress of marine engineering operations,autonomous underwater vehicles(AUVs)have been widely used in offshore oil pipeline inspection,hull inspection,marine surveying,underwater archaeology and other fields.The AUV system has non-linearity,uncertainty and external disturbances caused by hydrodynamics in the underwater environment.Therefore,higher requirements are put forward for the trajectory tracking control performance of the AUV system.Aiming at the AUV system with model uncertainties and external disturbances in this article,a trajectory tracking controller of AUV system is designed by using sliding mode control method and disturbance observation technology.The work of this article can be summarized in the following three parts:First,the fixed-time trajectory tracking control problem of an AUV system with model uncertainties and external disturbances is studied.1)Aiming at the AUV system without model uncertainties and external disturbances,a fixed-time integral sliding mode controller is proposed,which can ensure that the AUV can track the desired trajectory within a fixed time.2)Aiming at the AUV system with external disturbances,a fixed-time disturbance observer is designed to estimate the external disturbances,and the output value of the observer is used for feed-forward compensation.Then,a fixed-time integral sliding mode controller is proposed,which can compensate disturbance and have no chattering,so that the AUV can track the desired trajectory in a fixed time.3)A fixed-time lumped disturbance observer is proposed for AUV system with model uncertainties and external disturbances,and a fixed time integral sliding mode controller based on lumped disturbance observer is presented,which realizes fixed-time trajectory tracking of AUV.Finally,the effectiveness of the proposed method is verified by simulation and comparative.Second,the problem of fixed-time trajectory tracking control under prescribed performance constraints for the AUV system with model uncertainties and external disturbances is studied.Firstly,in order to improve the tracking performance of AUV system,a prescribed performance function is introduced to constrain the output tracking errors;secondly,a fixed-time extended state observer is designed to estimate the unknown system state and lumped disturbances,where the lumped disturbances include external disturbances and model uncertainties;thirdly,a fixed-time continuous sliding mode output feedback controller is implemented based on the output values of the observer and then the fixed-time trajectory tracking of the AUV is realized;finally,the simulation results demonstrate the effectiveness and superiority of the proposed method.Third,the problem of fixed-time trajectory tracking control of AUV system in the presence of external disturbances and model uncertainties is studied.Firstly,a fixed-time extended state observer is designed to estimate the external disturbances and model uncertainties;secondly,a new non-singular terminal sliding mode surface is constructed based on the output value of the observer,and a fixed-time non-singular terminal sliding mode controller is designed according to the sliding mode surface,thereby realizing the fixed-time trajectory tracking of the AUV system;finally,the simulation verifies that the proposed controller can obtain satisfactory control performance.